* At the tissues: When oxygen is unloaded from hemoglobin and carbon dioxide (CO2) is loaded, CO2 reacts with water to form carbonic acid (H2CO3). This process is catalyzed by the enzyme carbonic anhydrase. Carbonic acid then dissociates into bicarbonate ions (HCO3-) and hydrogen ions (H+).
* The chloride shift: To maintain neutrality, bicarbonate ions (HCO3-) diffuse out of the red blood cell into the plasma. To balance the charge, chloride ions (Cl-) move into the red blood cell. This exchange is known as the chloride shift.
* At the lungs: The process reverses. Bicarbonate ions move back into the red blood cell, chloride ions move out, and CO2 is released from the red blood cell and exhaled.
Essentially, the chloride shift is a mechanism to move bicarbonate ions out of the red blood cell in exchange for chloride ions, helping to maintain a balance of charges and facilitate CO2 transport.
